Gk = rand(1);
Rk = rand(1);
Pk = rand(1);

disp(1/(Gk*(1/Rk)*Gk + 1/ Pk))

Kk = Pk*Gk*1/(Gk*Pk*Gk + Rk);
disp((1-Kk*Gk) * Pk)

%Well it's indeed correct